Project 4 will focus on regional perfusion patterns in patients with dementia of the Alzheimer's type (AD). One-hundred and twenty-five questionable cases of AD (CDR = 0.5) and 40 normal controls (CDR = 0.) will be followed for a minimum of three years. It is anticipated that approximately 2/3 of the questionable cases (n = 80) will be categorized as AD by the end of the followup. This will permit an examination of the differences in cerebral perfusion as measured by SPECT between questionable cases who were diagnosed as AD on followup and questionable cases who were not. A variety of statistical techniques will be employed to evaluate the SPECT perfusion patterns both visually and quantitatively. These techniques will also permit the evaluation of the relationship between MRI measures, neuropsychological test scores, quantified EEGs and Eps and single photon emission computed tomography.